Embodiments of the disclosure relate generally to systems and methods of unified common mode voltage injection to achieve multiple functions.
Power converters, particularly multi-level power converters, are increasingly used for performing power conversion in a wide range of applications due to the advantages of high power quality waveform and high voltage capability. For example, multi-level power converters may be used for performing DC-to-AC power conversion to supply single-phase or multi-phase AC voltages to electric motors in vehicles and/or pumps. Multi-level converters may also be used in power generation systems such as wind turbine generators and solar generators for performing DC-to-AC power conversion to supply single-phase or multi-phase AC voltages for power grid transmission and distribution.
Typically, the power converters are designed to regulate or control various characteristic parameters in association with the operation of the power converters to meet certain requirements and/or ensure reliable operations. For example, a neutral point current between at least two DC capacitors on a DC link is controlled to minimize a voltage difference between the two DC capacitors to avoid stressing of the switching devices and/or creation of undesired harmonic signals. The neutral point current balancing is achieved by multiple control strategies, one of which includes injecting a common mode voltage in the multi-level converter to balance the neutral point current. However, different control strategies are applied to determine the common mode voltage for different level converters. For example, a control strategy for a three level converter is different from a control strategy for a seven level converter which results in undesirable costs and computations. In one approach, a unified common mode voltage injection technique may be applied to control the neutral point current in n-level converters. Different local optimum limits corresponding to different level converters may be used during computation of the common mode voltage to balance the neutral point current. And the calculation methods of neutral point current are different for different level converters as well because of different switching functions and different switching states. Such an approach leads to complex computations as computation methods for balancing the neutral point current are different for different level converters as each converter includes different switching functions and switching states.
Hence, there is a need for an improved system and control methodology to address the aforementioned issues.